The present invention relates to a liquid crystal display device; and, more particularly, the invention relates to an active matrix liquid crystal display device of the thin film transistor (hereinafter referred to as xe2x80x9cTFTxe2x80x9d) type or the like, and a method of manufacture thereof.
A liquid crystal display device, in view of the fact that the device is thin, light-weight and exhibits low power consumption, has been popularly used as a display device for displaying image information and character information in information handling equipment, such as a personal computer, a portable information terminal, a portable telephone, a digital camera, or visual equipment, such as a camera-built-in type VTR deck. Recently, along with the spread of large-capacity media and the start of BS digital broadcasting with the advent of DVD and the rapid progress in the development of large-capacity magnetic drives, the fusion of the personal computer and video digital media is in development, resulting in an increased demand for an image display device having a high image quality which can cope with such an application. A liquid crystal display adopting an in-plane switching (IPS) mode, which applies a lateral electric field to liquid crystal sealed in a gap between upper and lower substrates, has been recognized as a display method which is capable of satisfying such a demand for a high image quality, and various improvements have been made which promise further enhancement of the image quality.
On the other hand, along with the spread of portable telephones and portable information terminals, there has been an increased demand for various types of liquid crystal devices, ranging from medium-sized or small-sized liquid crystal display devices, which exhibit extremely low power consumption, to large-sized displays, including wall hanging television sets.
In a liquid crystal display device adopting the IPS mode, as disclosed in Japanese Laid-open Patent Publication 36058/1995, a method which performs switching of the liquid crystal using a lateral electric field, which is generated between two layered metal electrodes sandwiching an insulation film, has been most popularly used. However, there is a problem with such a structure in that, compared to a display device adopting the usual TN method, it is difficult to increase the aperture ratio of pixels, so that the light utilization efficiency is low. Since it is necessary to increase the brightness of the backlight to compensate for this defect, in such an LCD module it is difficult to attain the low power consumption which is demanded in a notebook type personal computer or a portable terminal.
To solve such a problem, in Japanese Laid-open Patent Publication 230378/1997, a method has been proposed in which pixel electrodes and a common electrode are arranged on an organic resin via through holes formed in the organic resin.
Further, as active elements for performing switching, TFTs using polysilicon have been known, besides TFTs using amorphous silicon.
The IPS type liquid crystal display device has a low aperture ratio; and, hence, there has been a demand for a high aperture ratio, that is, a high transmissivity.
One advantage of the present invention lies in the fact that, in an IPS type liquid crystal display device using low-temperature polysilicon TFTs as pixel TFTs, by eliminating metal common electrode lines, which have been arranged conventionally in one pixel region in parallel with gate lines so as to enhance the aperture ratio (transmissivity), it is also possible to ensure a sufficient holding capacitance to prevent the lowering of the liquid crystal potential when light from the backlight is irradiated on the polysilicon. Further, another advantage of the present invention lies in the fact that short-circuiting between an electrode which forms the holding capacitance and a drain line can be prevented.
Other advantages of the present invention will become apparent from the following description in this specification. Some typical examples of the present invention are as follows.
(1)
In a liquid crystal display device having a liquid crystal layer and a color filter layer, which are sandwiched by a first substrate and a second substrate, having a plurality of gate lines, a plurality of drain lines which cross the plurality of gate lines in a matrix array, and thin film transistors which are formed corresponding to respective intersections of the gate lines and the drain lines on the first substrate, so that each pixel is formed in a region surrounded by neighboring gate lines and neighboring drain lines, the first substrate includes semiconductor layers constituting the thin film transistors, a first insulation film formed on the semiconductor layers, a second insulation film formed on the first insulation film, and common lines formed on the second insulation film, and the second insulation film includes removal regions, which are positioned in regions where the semiconductor layers are formed, and a holding capacitance is formed by a common potential supplied from the common lines in the removal region and a pixel potential formed by the semiconductor layer.
(2)
In a liquid crystal display device having a liquid crystal layer and a color filter layer, which are sandwiched by a first substrate and a second substrate, having a plurality of gate lines, a plurality of drain lines which cross the plurality of gate lines in a matrix array, and thin film transistors which are formed corresponding to respective intersections of the gate lines and the drain lines on the first substrate, so that each pixel is formed in a region surrounded by neighboring gate lines and neighboring drain lines, the liquid crystal display device includes common electrodes and pixel electrodes which are formed on the first substrate in the same layer, and the common electrodes and the pixel electrodes are arranged over the gate lines to face each other in a spaced-apart manner by way of an insulation film.
(3)
In a lateral electric field liquid crystal display device having a liquid crystal layer and a color filter layer, which are sandwiched by a first substrate and a second substrate, having a plurality of gate lines, a plurality of drain lines which cross the plurality of gate lines in a matrix array, and thin film transistors which are formed corresponding to respective intersections of the gate lines and the drain lines on the first substrate, so that each pixel is formed in a region surrounded by neighboring gate lines and neighboring drain lines, wherein each pixel includes a common electrode and a pixel electrode formed on the first substrate, a source electrode of each thin film transistor is, extended to the neighboring gate line without crossing over the common electrode or a common electrode line, this neighboring gate line being different from the gate line over which the thin film transistor is formed, and a holding capacitance is formed between one electrode which is the gate line of a preceding row and another electrode which is the source electrode.
Further examples of the present invention will be apparent from the embodiments of the present invention which will be explained hereinafter.